December 4, 20205 yr Hi guys, After much deliberation, I managed to purchase a new cylinder kit from molinari in Italy.. on looking to fit, I have found that the piston is a type B of 72.451. I've measured the cylinder and get 72.48/9. On working the tolerance , I get near 0.030mm ... which is around 1 thou.. Will this seize ?
December 4, 20205 yr Possibly the piston, being the smaller metal object will expand more due to heat that the cylinder, which also benefits from its cooling. Id say the tolerances were too close, and you'd need a bit more. Have you contacted John Lampkins for proper advice, they'd know for sure!
December 4, 20205 yr Not wanting to split hairs but 0.030mm is in fact 0.75 thou inch so I would say much too tight.
December 4, 20205 yr Author Does anyone know offhand, what a new cylinder measures? I'm getting 72.48 with telescopic guages and calipers...
December 4, 20205 yr Think it's too tight,0.05mm would be better.Is the cylinder or old piston marked A,B,C ?
December 4, 20205 yr Author Piston is new and marked 72.457. Cylinder is also new which is why I'm slightly worried about the clearance! The seller in Italy states it's paired what ever that means
December 4, 20205 yr Author The skirt diameter for an A piston is 72.451, so that's why I can't understand how I've got a B piston bud
December 6, 20205 yr My apologies, you are correct, I got my conversion turned around, I still think it’s too tight though. I have a feeling that 0.001” per inch of cylinder bore has been a guide.
December 6, 20205 yr On 12/4/2020 at 9:45 AM, DAICROCKet said: Does anyone know offhand, what a new cylinder measures? I'm getting 72.48 with telescopic guages and calipers... Will will never measure it correctly with a Caliper You need a bore gauge and micrometer to get the correct measurement (a mic that measures 0.001mm) Good quality feeler gauges would probably give a better clearance measurement, if you cannot use the above 250cc bores normally need between 0.04 to 0.05mm clearance Edited December 6, 20205 yr by suzuki250
December 6, 20205 yr Author Thanks for the info guys... I've read many threads stating 1 thou per inch = 0.0028 for a 72.48mm bore. So If the piston is 72.457mm leaving a tolerance of 0.023mm equating to .0009 of a thou!! So if I put a standard 72.451mm equating to 0.029mm or 0.00114 I'm confused as that would also be tight!! Does anyone know where I can access beta tolerance data? Am I measuring the bore wrong as it is stated as 72.5??
December 6, 20205 yr Author I've tried feelers with piston top flush and guess what.. can't get a 1.5 thou down there!!
December 6, 20205 yr 5 hours ago, DAICROCKet said: Thanks for the info guys... I've read many threads stating 1 thou per inch = 0.0028 for a 72.48mm bore. So If the piston is 72.457mm leaving a tolerance of 0.023mm equating to .0009 of a thou!! So if I put a standard 72.451mm equating to 0.029mm or 0.00114 I'm confused as that would also be tight!! Does anyone know where I can access beta tolerance data? Am I measuring the bore wrong as it is stated as 72.5?? The bore is 72.5mm + or - whatever the tolerance is for the plating, (that's why they have size graded pistons) the clearance depends on the piston material, if its hypereutectic then 0.023 would be fine Measuring it with a caliper you cannot get the accuracy required, therefore if the seller says they are paired, then its probably correct. Build it and ride it Edited December 6, 20205 yr by suzuki250
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